Abstract
Isomeric 2,9-bis(amionmethyl)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) and -4,11-dienenickel(II) complexes (1−4) were studied by cyclic voltammetry. The thermodynamic stability of NiIII was the greatest in complex 4 with a trans configuration of the pendant amino groups. On acidification, the NiII/NiIII redox process was not observed. After alkalisation the redox process was only recovered in complex 4. The kinetics of the two-step macrocyclic ring isomerisation in 1 M HCl and DCl was studied, as a function of temperature, by UV/Vis and 1H NMR techniques. The energies of activation for the isomerisation of the cyclam ring from trans-V (5α) to trans-II (5β) and from trans-II to trans-I (5γ) were equal to 22.6 and 26.9 kcal mol−1, respectively.
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